Comparison of Py-GC/FID and Wet Chemistry Analysis for Lignin Determination in Wood and Pulps from Eucalyptus globulus

Abstract

The kraft pulps produced from heartwood and sapwood of Eucalyptus globulus at 130 ºC, 150 ºC, and 170 ºC were characterized by wet chemistry (total lignin as sum of Klason and soluble lignin fractions) and pyrolysis (total lignin denoted as py-lignin). The total lignin content obtained with both methods was similar. In the course of delignification, the py-lignin values were higher (by 2 to 5%) compared to Klason values, which is in line with the importance of soluble lignin for total lignin determination. Pyrolysis analysis presents advantages over wet chemical procedures, and it can be applied to wood and pulps to determine lignin contents at different stages of the delignification process. The py-lignin values were used for kinetic modelling of delignification, with very high predictive value and results similar to those of modelling using wet chemical determinations.

Recent innovations in analytical methods for the qualitative and quantitative assessment of lignin

“…The authors concluded that vanillin, isoeugenol, dihydroconiferyl alcohol, and G-C ¼ C ¼C structures that separate spruce and larch from pine. E. globulus total lignin content was measured using pyGC-FID [240]. This study measured a strong linear correlation (R 2 ¼0.979) between wet chemistry total lignin and pyGC-FID, regardless of the pulping conditions.…”

“…Thermochemical techniques have occasionally been utilized for the measurement of total lignin content [66,[238][239][240]. Alves and co-authors utilized analytical pyrolysis and GC-FID to measure the lignin content of a variety of hard-and softwoods [66,238,239].…”

“…S/G lignin ratios have proven to be important parameters for gauging the recalcitrance of lignin, although no clear trend has been established as to whether or not a high S content results in increased monomeric sugar release following an enzymatic hydrolysis. The traditional methods for measuring lignin monomer composition include NMR, pyGCMS, pyMBMS, and various wet chemical methods such as nitrobenzene oxidation (NBO) and thioacidolysis [4,5,13,56,58,59,[61][62][63][64][65][66]68,70,126,135,157,159,183,240,242,[291][292][293][294][295][296][297][298][299][300][301][302][303][304][305][306][307]. Common pyrolysis and mass spectral fragments are listed in Table 8, and illustrated in Fig.…”

“…Thermochemical evaluations of lignin monomers have become increasing prevalent [4,5,13,59,[61][62][63][64][65][66]68,70,126,157,159,183,240,242,293,295,[298][299][300][301]303,305,306,308]. When heated, lignin linkages are cleaved, permitting the identification of individual monomeric moieties.…”

High-Throughput Prediction of Acacia and Eucalypt Lignin Syringyl/Guaiacyl Content Using FT-Raman Spectroscopy and Partial Least Squares Modeling

“…The distinctive bands of S and G lignin, as well as cellulose, can be eliminated as correlative to these vibrational modes. Although its content in hardwoods is often minute, Acacia and Eucalyptus species have been determined to contain potentially 2-9 % H lignin, depending on the age of the trees [18][19][20][21]. Further chemical or instrumental analysis, such as thioacidolysis or 2D nuclear magnetic resonance, is required to determine if these vibrational modes correspond to H lignin.…”